This invention relates generally to glass fiber optics, and particularly, relates to a process of fabricating fibers useful in nonlinear optics applications.
Previous nonlinear optical fibers have relied on 4-wave mixing in glass fibers, doping of glass fiber claddings, or cores, or liquid core fibers. Phase-matched 3-wave mixing (frequency doubling, summation or difference generation and parametric amplification) has never been achieved in glass fibers. Although planar waveguides have been used for frequency doubling, their efficiency is limited by short interaction length and high losses coupling into and out of such structures. Also, the use of planar guides in certain fiber optic systems is restricted by differences in the guide shapes themselves corresponding to differences in their mode structures.
For example, in conventional fiber optics, light is guided by total internal reflection in a filament of glass having a glass cladding of lower index fused on the light-carrying core to provide a good interface at which reflection occurs. When a doped cladding is applied to a passive core, and the cladding has a lower index, a small portion of the light penetrates into the lower index cladding in the form of an evanescent wave. Depending on the type of cladding, oscillations and amplification of the input light signal may occur.
Frequency doubling has been obtained in planar optical waveguides using nonlinear interactions therein. For example, a thin film of LiNbO.sub.3 was rf-sputtered onto a sapphire substrate. Tunable laser radiation was coupled into this guide and phase-matched and frequency up-conversion was obtained with an efficiency of about 10.sup.-3. The problem associated with this method was that there is a short interaction length. The use of planar waveguides in fiber optics systems is unlikely because of the short interaction distance and the problems associated therewith.
The present invention is directed toward providing a process of fabricating hybrid single crystal optical fibers for frequency conversion and amplification in which the above undesirable characteristics are minimized.